From: nobu.nokada@...
Date: 2001-11-29T12:50:09+09:00
Subject: [ruby-talk:26860] Re: overload possible?

At Thu, 29 Nov 2001 08:13:36 +0900,
Harry Ohlsen <harryo@zipworld.com.au> wrote:
> It IS a little messy, though, in that you have to sacrifice a class
> variable for the return value.  Hmmm ... maybe Robert's version
> is looking simpler now :-).

What about this.

module Overload
  class Argument
    Separator = ",".freeze
    attr_reader :signature
    def initialize(sig, args)
      @signature = sig
      @arguments = args
    end
    def dispatch(*types, &block)
      if @signature == types.join(Separator)
	throw :dispatched, yield(*@arguments)
      end
    end
  end

  def overload(args)
    args = Argument.new(args.collect {|a| a.type.to_s}.join(Argument::Separator), args)
    catch(:dispatched) {
      yield args
      raise TypeError, "bad set of arguments, #{args.signature}"
    }
  end
end

if __FILE__ == $0
  class Fred
    include Overload
    
    def hello(*args)
      overload(args) do |args|
	args.dispatch(:Fixnum, :String, :Float) do
	  |i, s, f|
	  puts "(Fixnum, String, Float) -> [ #{i}, \"#{s}\", #{f} ]"
	  "1"
        end
	args.dispatch(:String, :Fixnum) do
	  |i, s|
	  puts "(String, Fixnum) -> [ \"#{s}\", #{i} ]"
	  "2"
        end
      end
    end
    
  end
  
  f = Fred.new
  
  puts "f1 = "+f.hello(123, "hello", 123.456)
  puts "f2 = "+f.hello("hello", 123)
  begin
    f.hello("abc", "def")
  rescue TypeError
    puts "f3 = "+$!
  end
end

Nobu Nakada